Inducing Differential Self-Assembling Behavior in Ultrashort Peptide Hydrogelators Using Simple Metal Salts

Ag+-Induced Supramolecular Polymers of Folic Acid: Reinforced by External Kosmotropic Anions Exhibiting Salting Out

Introducing kosmotropic salts enhances protein stability and reduces solubility by withdrawing water from the protein surface, leading to 'salting out', a phenomenon we have mimicked in supramolecular polymers (SPs). Under the guidance of Ag+, folic acid (FA) self-assembled in water through slipped-stacking and hydrophobic interactions into elongated, robust one-dimensional SPs, resulting in thermo-stable supergels. The SPs exhibited temperature and dilution tolerance, attributed to the stability of the FA-Ag+ complex and its hydrophobic stacking. Importantly, FA-Ag+ SP's stability has been augmented by the kosmotropic anions, such as SO42-, strengthening hydrophobic interactions in the SP, evident from the enhanced J-band, causing improvement of gel's mechanical property. Interestingly, higher kosmotrope concentrations caused a significant decrease in SP's solubility, leading to precipitation of the reinforced SPs─a 'salting out' effect. Conversely, chaotropes like ClO4- slightly destabilized hydrophobic stacking and promoted an extended conformation of individual SP chain with enhanced solubility, resembling a 'salting in' effect.

Designing Pathway-Controlled Multicomponent Ultrashort Peptide Hydrogels with Diverse Functionalities at the Nanoscale for Directing Cellular Behavior

Tuning self-assembling pathways by implementing different external stimuli has been extensively studied, owing to their effective control over structural and mechanical properties. Consequently, multicomponent peptide hydrogels with high structural tunability and stimuli responsiveness are crucial in dictating cellular behavior. Herein, we have implemented both coassembly approach and pathway-dependent self-assembly to design nonequilibrium nanostructures to understand the thermodynamic and kinetic aspects of peptide self-assembly toward controlling cellular response. Our system involved an ultrashort peptide gelator and a hydrophilic surfactant which coassembled through different pathways, i.e., heat-cool and sonication methods with variable energy input. Interestingly, it was possible to access diverse structural and mechanical properties at the nanoscale in a single coassembled system. Further, the hydrophilic surfactant provided additional surface functionalities, thus creating an efficient hydrophilic matrix for cellular interaction. Such diverse functionalities in a single coassembled system could lead to the development of advanced scaffolds, with applications in various biomedical fields.

Self-Assembled Food Peptides: Recent Advances and Perspectives in Food and Health Applications

Self-assembling peptides are rapidly gaining attention as novel biomaterials for food and biomedical applications. Peptides self-assemble when triggered by physical or chemical factors due to their versatile physicochemical characteristics. Peptide self-assembly, when combined with the health-promoting bioactivity of peptides, can also result in a plethora of biofunctionalities of the biomaterials. This perspective highlights current developments in the use of food-derived self-assembling peptides as biomaterials, bioactive nutraceuticals, and potential dual functioning bioactive biomaterials. Also discussed are the challenges and opportunities in the use of self-assembling bioactive peptides in designing biocompatible, biostable, and bioavailable multipurpose biomaterials.

Recent advances in peptide-based bioactive hydrogels for nerve repair and regeneration: from material design to fabrication, functional tailoring and applications

The injury of both central and peripheral nervous systems can result in neurological disorders and severe nervous diseases, which has been one of the challenges in the medical field. The use of peptide-based hydrogels for nerve repair and regeneration (NRR) provides a promising way for treating these problems, but the effects of the functions of peptide hydrogels on the NRR efficiency have been not understood clearly. In this review, we present recent advances in the material design, matrix fabrication, functional tailoring, and NRR applications of three types of peptide-based hydrogels, including pure peptide hydrogels, other component-functionalized peptide hydrogels, and peptide-modified polymer hydrogels. The case studies on the utilization of various peptide-based hydrogels for NRR are introduced and analyzed, in which the effects and mechanisms of the functions of hydrogels on NRR are illustrated specifically. In addition, the fabrication of medical NRR scaffolds and devices for pre-clinical application is demonstrated. Finally, we provide potential directions on the development of this promising topic. This comprehensive review could be valuable for readers to know the design and synthesis strategies of bioactive peptide hydrogels, as well as their functional tailoring, in order to promote their practical applications in tissue engineering, biomedical engineering, and materials science.

Water-Based Synthesis of β-Sheet-Like Supramolecular Metallohydrogel Organized by Using a Native Ultrashort Peptide Sequence

Designing supramolecular hydrogels using short peptides is challenging. To control self-assembly, a certain amount of organic solvent is typically added to the system, or the short peptide is modified with a functional group that is hydrophobic, hydrophilic, or highly coordinative. We discovered that l-His-l-Ile-l-Thr (HIT), a very short unmodified "native" tripeptide, selectively responds to Cu2+ ions in pure water to form a transparent supramolecular metallohydrogel. Circular dichroism analysis revealed that Cu2+ ions, but no other metal species, caused HIT to change from a random-coil-like to a β-sheet-like structure. Other spectroscopic methods were used to characterize the properties of the supramolecular metallohydrogel. These results are expected to facilitate the development of native short peptides as advanced functional biomaterials.

Designing Cardin-Motif Peptide and Heparin-Based Multicomponent Advanced Bioactive Hydrogel Scaffolds to Control Cellular Behavior

Recently, peptide and sugar-based multicomponent systems have gained much interest in attaining the sophisticated structure and biofunctional complexity of the extracellular matrix (ECM). To this direction, we have designed for the first time a biologically relevant minimalist Cardin-motif peptide capable of binding ECM-derived glycosaminoglycans. Herein, we explored Cardin-motif peptide and heparin-based biomolecular matrix by employing simple noncovalent interactions at the molecular level. Interestingly, this peptide was inadequate to induce hydrogelation at ambient pH due to the presence of basic amino acids. However, addition of heparin successfully triggered its gelation at physiological pH following favorable electrostatic interactions with heparin. Importantly, the newly developed scaffolds displayed tunable nanofibrous morphology and superior mechanical properties as controlled simply by the differential mixing ratio of both biomolecular entities. Additionally, these composite scaffolds could closely mimic the complexity of ECM as they demonstrated superior biocompatibility and enhanced growth and proliferation of neural cells as compared to the peptide scaffold.

Electrochemical Wearable Biosensors and Bioelectronic Devices Based on Hydrogels: Mechanical Properties and Electrochemical Behavior

Hydrogel-based wearable electrochemical biosensors (HWEBs) are emerging biomedical devices that have recently received immense interest. The exceptional properties of HWEBs include excellent biocompatibility with hydrophilic nature, high porosity, tailorable permeability, the capability of reliable and accurate detection of disease biomarkers, suitable device-human interface, facile adjustability, and stimuli responsive to the nanofiller materials. Although the biomimetic three-dimensional hydrogels can immobilize bioreceptors, such as enzymes and aptamers, without any loss in their activities. However, most HWEBs suffer from low mechanical strength and electrical conductivity. Many studies have been performed on emerging electroactive nanofillers, including biomacromolecules, carbon-based materials, and inorganic and organic nanomaterials, to tackle these issues. Non-conductive hydrogels and even conductive hydrogels may be modified by nanofillers, as well as redox species. All these modifications have led to the design and development of efficient nanocomposites as electrochemical biosensors. In this review, both conductive-based and non-conductive-based hydrogels derived from natural and synthetic polymers are systematically reviewed. The main synthesis methods and characterization techniques are addressed. The mechanical properties and electrochemical behavior of HWEBs are discussed in detail. Finally, the prospects and potential applications of HWEBs in biosensing, healthcare monitoring, and clinical diagnostics are highlighted.

Rational Design and Self-Assembly of Histidine-Rich Peptides on a Graphite Surface

Histidine-rich peptides (HRPs) have been investigated to create functional biomolecules based on the nature of histidine, such as ion binding and catalytic activity. The organization of these HRPs on a solid surface can lead to surface functionalization with the well-known properties of HRPs. However, immobilization of HRPs on the surface has not been realized. Here, we design a series of octapeptides with histidine repeat units, aiming to establish their self-assembly on a graphite surface to produce a highly robust and active nanoscaffold. The new design has (XH)₄, and we incorporated various types of hydrophobic amino acids at X in the sequence to facilitate their interaction with the surface. The effect of the pair of amino acids on their self-assembly was investigated by atomic force microscopy. Contact angle measurement revealed that these assemblies functionalized graphite surfaces with different wetting chemistry. Moreover, the secondary structure of peptides was characterized by Fourier transform infrared spectroscopy (FTIR), which gives us further insights into the conformation of histidine repeat peptides on the surface. Our results showed a new approach to applying histidine-rich peptides on the surface and tuning the self-assembly behavior by introducing different counter amino acids that could be integrated with a wide range of biosensing and biotechnology applications.

Designing ECM-inspired supramolecular scaffolds by utilizing the interactions between a minimalistic neuroactive peptide and heparin

Short bioactive peptide-based supramolecular hydrogels are emerging as interesting candidates for developing scaffolds for tissue engineering applications. However, proteins and peptides represent only a single class of molecules present in the native ECM, thus, recapitulating the complete ECM microenvironment via only peptide-based biomaterials is extremely challenging. In this direction, complex multicomponent-based biomaterials have started gaining importance for achieving the biofunctional complexity and structural hierarchy of the native ECM. Sugar-peptide complexes can be explored in this direction as they provide essential biological signaling required for cellular growth and survival in vivo. In this direction, we explored the fabrication of an advanced scaffold by employing heparin and short bioactive peptide interactions at the molecular level. Interestingly, the addition of heparin into the peptide has significantly modulated the supramolecular organization, nanofibrous morphology and the mechanical properties of the scaffold. Additionally, the combined hydrogels demonstrated superior biocompatibility as compared to the peptide counterpart at certain ratios. These newly developed scaffolds were also observed to be stable under 3-D cell culture conditions and supported cellular adhesion and proliferation. Most importantly, the inflammatory response was also minimized in the case of combined hydrogels as compared to heparin. We expect that this approach of using simple non-covalent interactions between the ECM-inspired small molecules to fabricate biomaterials with improved mechanical and biological properties could advance the current knowledge on designing ECM mimetic biomaterials. Such an attempt would create a novel, adaptable and simplistic bottom-up strategy for the invention of new and more complex biomaterials of ECM origin with advanced functions.

Molecularly Stimuli-Responsive Self-Assembled Peptide Nanoparticles for Targeted Imaging and Therapy

Self-assembly has emerged as an extensively used method for constructing biomaterials with sizes ranging from nanometers to micrometers. Peptides have been extensively investigated for self-assembly. They are widely applied owing to their desirable biocompatibility, biodegradability, and tunable architecture. The development of peptide-based nanoparticles often requires complex synthetic processes involving chemical modification and supramolecular self-assembly. Stimuli-responsive peptide nanoparticles, also termed "smart" nanoparticles, capable of conformational and chemical changes in response to stimuli, have emerged as a class of promising materials. These smart nanoparticles find a diverse range of biomedical applications, including drug delivery, diagnostics, and biosensors. Stimuli-responsive systems include external stimuli (such as light, temperature, ultrasound, and magnetic fields) and internal stimuli (such as pH, redox environment, salt concentration, and biomarkers), facilitating the generation of a library of self-assembled biomaterials for biomedical imaging and therapy. Thus, in this review, we mainly focus on peptide-based nanoparticles built by self-assembly strategy and systematically discuss their mechanisms in response to various stimuli. Furthermore, we summarize the diverse range of biomedical applications of peptide-based nanomaterials, including diagnosis and therapy, to demonstrate their potential for medical translation.

π-System Functionalization Transforms Amyloidogenic Peptide Fragment of Human Islet Amyloid Polypeptide into a Super Hydrogelator

While a considerable number of ultra-short/short amyloid peptides have been reported to form 3D supramolecular hydrogels, they all possess high minimum gelation concentration (MGC) (≥1 wt%), which preclude their applications. In this context, we demonstrate that functionalisation of a well-known amyloidogenic ultra-short peptide fragment NFGAIL (IAPf) of human Islet amyloid polypeptide with a π-system (Fluorenyl, Fm) at the N-terminus of the peptide (Fm-IAPf) yield not only highly thermostable hydrogel at physiological pH but also exhibited super gelator nature as the MGC (0.08 wt%) falls below 0.1 wt%. Various experimental results confirmed that aromatic π-π interactions from fluorenyl moieties and hydrogen bonding interactions between the IAPf drive the self-assembly/fibril formation. Fm-IAPf is the first super hydrogelator derived from amyloid-based ultra-short peptides, to the best of our knowledge. We strongly believe that this report, i. e., functionalization of an amyloid peptide with π-system, provides a lead to develop super hydrogelators from other amyloid-forming peptide fragments for their potential applications.

Peptide-Based Materials That Exploit Metal Coordination

Metal-ion coordination has been widely exploited to control the supramolecular behavior of a variety of building blocks into functional materials. In particular, peptides offer great chemical diversity for metal-binding modes, combined with inherent biocompatibility and biodegradability that make them attractive especially for medicine, sensing, and environmental remediation. The focus of this review is the last 5 years' progress in this exciting field to conclude with an overview of the future directions that this research area is currently undertaking.

Anion Effects on the Supramolecular Self-Assembly of Cationic Phenylalanine Derivatives

Supramolecular hydrogels have emerged as a class of promising biomaterials for applications such as drug delivery and tissue engineering. Self-assembling peptides have been well studied for such applications, but low molecular weight (LMW) amino acid-derived gelators have attracted interest as low-cost alternatives with similar emergent properties. Fluorenylmethyloxycarbonyl-phenylalanine (Fmoc-Phe) is one such privileged motif often chosen due to its inherent self-assembly potential. Previously, we developed cationic Fmoc-Phe-DAP gelators that assemble into hydrogel networks in aqueous NaCl solutions of sufficient ionic strength. The chloride anions in these solutions screen the cationic charge of the gelators to enable self-assembly to occur. Herein, we report the effects of varying the anions of sodium salts on the gelation potential, nanoscale morphology, and hydrogel viscoelastic properties of Fmoc-Phe-DAP and two of its fluorinated derivatives, Fmoc-3F-Phe-DAP and Fmoc-F₅-Phe-DAP. It was observed that both the anion identity and gelator structure had a significant impact on the self-assembly and gelation properties of these derivatives. Changing the anion identity resulted in significant polymorphism of the nanoscale morphology of the assembled states that was dependent on the chemical structure of the gelator. The emergent viscoelastic character of the hydrogel networks was also found to be reliant on the anion identity and gelator structure. These results demonstrate the complex interplay between the gelator and environment that have a profound and often unpredictable impact on both self-assembly properties and emergent viscoelasticity in supramolecular hydrogels formed by LMW compounds. This work also illustrates the current lack of understanding that limits the rational design of potential biomaterials that will be in contact with complex biological fluids and provides motivation for additional research to correlate the chemical structure of LMW gelators with the structure and emergent properties of the resulting supramolecular assemblies as a function of environment.

Biomass-derived cellulose nanofibers and iron oxide-based nanohybrids for thermal insulation application

In recent years, due to high energy consumption in the building sector and subsequent environmental issues, environment-friendly and cost-effective thermally insulating materials are in high demand to improve the energy efficiency of buildings. Current commercially available thermal insulating materials (polystyrene) always pose a challenge due to their non-biodegradability and poor insulating performance. To this end, biomass-derived aerogels are attracting significant interest as renewable and sustainable insulating materials. In this work, we have developed a facile strategy for synthesizing cellulose nanofibers from biomass-derived wood pulp as a cost-effective starting material by TEMPO-oxidation, and further incorporating iron oxide nanoparticles to make a nanohybrid. Interestingly, in these nanohybrids, the functional attributes like mechanical strength and flammability were improved to a great extent and thus overcoming the limitations of the commercially available thermal insulating materials in terms of their stability and durability. Most importantly, these nanohybrids demonstrated very low thermal conductivity, as low as 0.024 W m-1 K-1, indicating the better insulating potential of these nanohybrids as compared to other conventional insulating materials.

Exploring the TEMPO-Oxidized Nanofibrillar Cellulose and Short Ionic-Complementary Peptide Composite Hydrogel as Biofunctional Cellular Scaffolds

Multicomponent self-assembly is an emerging approach in peptide nanotechnology to develop nanomaterials with superior physical and biological properties. Inspired by the multicomponent nature of the native extracellular matrix (ECM) and the well-established advantages of co-assembly in the field of nanotechnology, we have attempted to explore the noncovalent interactions among the sugar and peptide-based biomolecular building blocks as an approach to design and develop advanced tissue scaffolds. We utilized TEMPO-oxidized nanofibrillar cellulose (TO-NFC) and a short ionic complementary peptide, Nap-FEFK, to fabricate highly tunable supramolecular hydrogels. The differential doping of the peptide into the TO-NFC hydrogel was observed to tune the surface hydrophobicity, microporosity, and mechanical stiffness of the scaffold. Interestingly, a differential cellular response was observed toward composite scaffolds with a variable ratio of TO-NFC versus Nap-FEFK. Composite scaffolds having a 10:1 (w/w) ratio of TO-NFC and the Nap-FEFK peptide showed enhanced cellular survival and proliferation under two-dimensional cell culture conditions. More interestingly, the cellular proliferation on the 10:1 matrix was found to be similar to that of Matrigel in three-dimensional culture conditions, which clearly indicated the potential of these hydrogels in advanced tissue engineering applications. Additionally, these composite hydrogels did not elicit any significant inflammatory response in Raw cells and supported their survival and proliferation, which further emphasized their ability to form versatile scaffolds for tissue regeneration. This multicomponent assembly approach to construct biomolecular composite hydrogels to access superior physical and biological properties within the scaffold is expected to improve the scope for designing novel ECM-mimicking biomaterials for regenerative medicine.

Mapping the Morphological Landscape of Oligomeric Di-block Peptide-Polymer Amphiphiles

Peptide-polymer amphiphiles (PPAs) are tunable hybrid materials that achieve complex assembly landscapes by combining the sequence-dependent properties of peptides with the structural diversity of polymers. Despite their promise as biomimetic materials, determining how polymer and peptide properties simultaneously affect PPA self-assembly remains challenging. We herein present a systematic study of PPA structure-assembly relationships. PPAs containing oligo(ethyl acrylate) and random-coil peptides were used to determine the role of oligomer molecular weight, dispersity, peptide length, and charge density on self-assembly. We observed that PPAs predominantly formed spheres rather than anisotropic particles. Oligomer molecular weight and peptide hydrophilicity dictated morphology, while dispersity and peptide charge affected particle size. These key benchmarks will facilitate the rational design of PPAs that expand the scope of biomimetic functionality within assembled soft materials.

Cooperative Metal Ion Coordination to the Short Self-Assembling Peptide Promotes Hydrogelation and Cellular Proliferation

Non-covalent interactions among short peptides and proteins led to their molecular self-assembly into supramolecular packaging, which provides the fundamental basis of life. These biomolecular assemblies are highly susceptible to the environmental conditions, including temperature, light, pH, and ionic concentration, thus inspiring the fabrication of a new class of stimuli-responsive biomaterials. Here, we report for the first time the cooperative effect of the divalent metal ions to promote hydrogelation in the short collagen inspired self-assembling peptide for developing advanced biomaterials. Introduction of the biologically relevant metal ions (Ca²⁺ /Mg²⁺ ) to the peptide surpasses its limitation to self-assemble into a multi-scale structure at physiological pH. In particular, in presence of metal ions, the negatively charged peptide showed a distinct shift in its equilibrium point of gelation and demonstrated conversion from sol to gel and thus enabling the scope of fabricating an advanced biomaterial for controlling cellular behaviour. Interestingly, tunable mechanical strength and improved cellular response were observed within ion-coordinated peptide hydrogels compared to the peptide gelator. Microscopic analyses, rheological assessment, and biological studies established the importance of utilizing a novel strategy by simply using metal ions to modulate the physical and biological attributes of CIPs to construct next-generation biomaterials. This article is protected by copyright. All rights reserved.

A Rapid Self-Assembly Peptide Hydrogel for Recruitment and Activation of Immune Cells

Self-assembly peptide nanotechnology has attracted much attention due to its regular and orderly structure and diverse functions. Most of the existing self-assembly peptides can form aggregates with specific structures only under specific conditions and their assembly time is relatively long. They have good biocompatibility but no immunogenicity. To optimize it, a self-assembly peptide named DRF3 was designed. It contains a hydrophilic and hydrophobic surface, using two N-terminal arginines, leucine, and two c-terminal aspartate and glutamic acid. Meanwhile, the c-terminal of the peptide was amidated, so that peptide segments were interconnected to increase diversity. Its characterization, biocompatibility, controlled release effect on antigen, immune cell recruitment ability, and antitumor properties were examined here. Congo red/aniline blue staining revealed that peptide hydrogel DRF3 could be immediately gelled in PBS. The stable β-sheet secondary structure of DRF3 was confirmed by circular dichroism spectrum and IR spectra. The observation results of cryo-scanning electron microscopy, transmission electron microscopy, and atomic force microscopy demonstrated that DRF3 formed nanotubule-like and vesicular structures in PBS, and these structures interlaced with each other to form ordered three-dimensional nanofiber structures. Meanwhile, DRF3 showed excellent biocompatibility, could sustainably and slowly release antigens, recruit dendritic cells and promote the maturation of dendritic cells (DCs) in vitro. In addition, DRF3 has a strong inhibitory effect on clear renal cell carcinoma (786-0). These results provide a reliable basis for the application of peptide hydrogels in biomedical and preclinical trials.

S-Benzyl Cysteine Based Cyclic Dipeptide Super Hydrogelator: Enhancing Efficacy of an Anticancer Drug via Sustainable Release

Peptide based low molecular weight supramolecular hydrogels hold promising aspects in various fields of application especially in biomaterial and biomedical sciences such as drug delivery, wound healing, tissue engineering, cell proliferation, etc due to their extreme biocompatibility. Unlike linear peptides, cyclic peptides have more structural rigidity and tolerance to enzymatic degradation and high environmental stability which make them even better candidates for the above said applications. Herein, a new small cyclic dipeptide (CDP) cyclo-(Leu-S-Bzl-Cys) (P1) consisting of L-leucine and S-benzyl protected L-cysteine was reported which formed hydrogel at physiological conditions (at 37^o C and pH=7.46). The hydrogel formed from the cyclic dipeptide P1 showed very good tolerance towards environmental parameters such as pH, temperature and was seen to be stable for more than a year without any deformation. The hydrogel was thermoreversible and stable in the pH range 6-12. Mechanical strength of P1 hydrogel was measured by rheology experiment. AFM and FE-SEM images revealed that in aqueous solvents P1 self-assembled into a highly cross-linked nanofibrillar network which immobilized water molecules inside the cages and formed the hydrogel. The self-assembled cyclic dipeptide acquired antiparallel β-sheet secondary structure which was evident from CD and FT-IR studies. The β-sheet arrangement and formation of amyloid fibrils were further established by ThT binding assay. Furthermore, P1 was able to form hydrogel in presence of anticancer drug 5-fluorouracil (5FU) and sustainable release of the drug from the hydrogel was measured in-vitro. The hydrogelator P1 showed almost no cytotoxicity towards human colorectal cancer cell line HCT116 up to a considerable high concentration and showed potential application in sustainable drug delivery. The co-assembly of 5FU and P1 hydrogel exhibited much better anticancer activity towards HCT116 cancer cell line than 5-fluorouracil alone and decreased the IC₅₀ dose of 5-fluorouracil to a much lower value.

A review of recent advances in metal ion hydrogels: mechanism, properties and their biological applications

The mechanisms, common properties and biological applications of different types of metal ion hydrogels are summarized.

Self-assembled di- and tripeptide gels for the passive entrapment and pH-responsive, sustained release of an antidiabetic drug, glimepiride

Diabetes is a global epidemic that poses a severe challenge to public health. The characteristic features of this disease are hyperglycemia and deterioration of the function of pancreatic β-cells, which...

Peptide Hydrogel with Antibacterial Performance Induced by Rare Earth Metal Ions

Metal ion-induced peptide assembly is an interesting field. As compared to traditional antibacterial Ag⁺, rare earth metal ions possess the advantage of antibacterial performance with photostability and low toxicity. Herein, a new peptide Fmoc-FFWDD-OH was designed and synthesized, which could form a stable hydrogel induced by rare earth metal ions, including Tb³⁺, Eu³⁺, and La³⁺. The mechanical properties were characterized by rheological measurements, and they exhibited elasticity-dominating properties. Transmission electron microscopy (TEM) images showed a large number of nanoscale fiber structures formed in the hydrogel. Circular dichroism (CD) spectra, Fourier transform infrared (FT-IR) spectra, ThT assays, and X-ray diffraction (XRD) pattern illustrated the formation mechanism of the fiber structure. The rare earth ion-induced peptide hydrogel was proved to possess good antibacterial performance on Escherichia coli (E. coli) with excellent biocompatibility. The introduction of rare earth metal ions may have some potential applications in the biological antibacterial and medical fields.

Designing aromatic N-cadherin mimetic short-peptide-based bioactive scaffolds for controlling cellular behaviour

The development of suitable biomaterials is one of the key factors responsible for the success of the tissue-engineering field. Recently, significant effort has been devoted to the design of biomimetic materials that can elicit specific cellular responses and direct new tissue formation mediated by bioactive peptides. The success of the design principle of such biomimetic scaffolds is mainly related to the cell-extracellular matrix (ECM) interactions, whereas cell-cell interactions also play a vital role in cell survival, neurite outgrowth, attachment, migration, differentiation, and proliferation. Hence, an ideal strategy to improve cell-cell interactions would rely on the judicious incorporation of a bioactive motif in the designer scaffold. In this way, we explored for the first time the primary functional pentapeptide sequence of the N-cadherin protein, HAVDI, which is known to be involved in cell-cell interactions. We have formulated the shortest N-cadherin mimetic peptide sequence utilizing a minimalistic approach. Furthermore, we employed a classical molecular self-assembly strategy through rational modification of the basic pentapeptide motif of N-cadherin, i.e. HAVDI, using Fmoc and Nap aromatic moieties to modify the N-terminal end. The designed N-cadherin mimetic peptides, Fmoc-HAVDI and Nap-HAVDI, self-assembled to form a nanofibrous network resulting in a bioactive peptide hydrogel at physiological pH. The nanofibrous network of the pentapeptide hydrogels resembles the topology of the natural ECM. Furthermore, the mechanical strength of the gels also matches that of the native ECM of neural cells. Interestingly, both the N-cadherin mimetic peptide hydrogels supported cell adhesion and proliferation of the neural and non-neural cell lines, highlighting the diversity of these peptidic scaffolds. Further, the cultured neural and non-neural cells on the bioactive scaffolds showed normal expression of β-III tubulin and actin, respectively. The cellular response was compromised in control peptides, which further establishes the significance of the bioactive motifs towards controlling the cellular behaviour. Our study indicated that our designer N-cadherin-based peptidic hydrogels mimic the structural as well as the physical properties of the native ECM, which has been further reflected in the functional attributes offered by these scaffolds, and thus offer a suitable bioactive domain for further use as a next-generation material in tissue-engineering applications.

Metal Cation Triggered Peptide Hydrogels and Their Application in Food Freshness Monitoring and Dye Adsorption

Metal-ligand interactions have emerged as an important tool to trigger and modulate self-assembly, and to tune the properties of the final supramolecular materials. Herein, we report the metal-cation induced self-assembly of a pyrene-peptide conjugate to form hydrogels. The peptide has been rationally designed to favor the formation of β-sheet 1D assemblies and metal coordination through the Glu side chains. We studied in detail the self-assembly process in the presence of H+, Li+, Na+, K+, Ca2+, Ni2+, Cu2+, Zn2+, Cd2+, Co2+, Fe3+, and Cr3+ and found that the morphology and mechanical properties of the hydrogels are ion-dependent. Moreover, thanks to the presence of the metal, new applications could be explored. Cu2+ metallogels could be used for amine sensing and meat freshness monitoring, while Zn2+ metallogels showed good selectivity for cationic dye adsorption and separation.

An overview of latest advances in exploring bioactive peptide hydrogels for neural tissue engineering

Neural tissue engineering holds great potential in addressing current challenges faced by medical therapies employed for the functional recovery of the brain. In this context, self-assembling peptides have gained considerable interest owing to their diverse physicochemical properties, which enable them to closely mimic the biophysical characteristics of the native ECM. Additionally, in contrast to synthetic polymers, which lack inherent biological signaling, peptide-based nanomaterials could be easily designed to present essential biological cues to the cells to promote cellular adhesion. Moreover, injectability of these biomaterials further widens their scope in biomedicine. In this context, hydrogels obtained from short bioactive peptide sequences are of particular interest owing to their facile synthesis and highly tunable properties. In spite of their well-known advantages, the exploration of short peptides for neural tissue engineering is still in its infancy and thus detailed discussion is required to evoke interest in this direction. This review provides a general overview of various bioactive hydrogels derived from short peptide sequences explored for neural tissue engineering. The review also discusses the current challenges in translating the benefits of these hydrogels to clinical practices and presents future perspectives regarding the utilization of these hydrogels for advanced biomedical applications.

Enzyme-Induced Supramolecular Order in Pyrene Dipeptide Hydrogels for the Development of an Efficient Energy-Transfer Template

Peptide self-assembly is gathering much attention due to the precise control it provides for the arrangement of functional moieties for the fabrication of advanced functional materials. It is desirable to use a physical, chemical, or biological trigger that can control the self-assembly process. In the current article, we have applied an enzyme to induce the peptide self-assembly of an aromatic peptide amphiphile, which modulates the supramolecular order in the final gel phase material. We accessed diverse peptide hydrogels from identical gelator concentrations by simply changing the enzyme concentration, which controlled the reaction kinetics and influenced the dynamics of self-assembly. Depending upon the concentration of the enzyme, a bell-shaped relationship was observed in terms of intermolecular interactions, morphology, and properties of the final gel phase material. The access of non-equilibrium structures was further demonstrated by fluorescence emission spectroscopy, circular dichroism spectroscopy, atomic force microscopy, transmission electron microscopy, and rheology. This strategy is applied to construct a charge-transfer hydrogel by doping the donor hydrogel with an acceptor moiety, which exhibits efficient energy transfer. Interestingly, such structural control at the nanoscopic level can further tune the energy-transfer efficiency by simply modulating the enzyme concentration.

Pathway-Dependent Preferential Selection and Amplification of Variable Self-Assembled Peptide Nanostructures and Their Biological Activities

We demonstrate the formation of diverse peptide nanostructures, which are "out of equilibrium" based on a single dipeptide gelator. These structures represent the differential energy states of the free energy landscape, which are accessed by differential energy inputs provided by variable self-assembly pathways, that is, heat-cool method or ultrasonication. A higher energy input by the heat-cool method created a thermodynamically favored long entangled nanofibrillar network, while twisted ribbonlike structures were prevalent by ultrasonication. Interestingly, the nanofibrillar network representing the global thermodynamic minima could be accessed by simply melting the kinetically trapped structures as indicated by the thermoreversibility studies. The impact on the material strength was remarkable; gels with an order of magnitude difference in mechanical properties could be fabricated by simply modulating the self-assembly pathways. Interestingly, the thermodynamically favored nanofibrous network promoted cellular adhesion and survival, while a significant number of cells fail to adhere on the kinetically trapped twisted ribbons. Thus, nonequilibrium nanostructures open up new directions to develop advanced functional materials with diverse functions.

Accessing Highly Tunable Nanostructured Hydrogels in a Short Ionic Complementary Peptide Sequence via pH Trigger

Creating diverse nanostructures from a single gelator through modulating the self-assembly pathway has been gaining much attention in recent years. To this direction, we are exploring the effect of modulation of pH as a potential self-assembly pathway in governing the physicochemical properties of the final gel phase material. In this context, we used a classical nongelator with the ionic complementary sequence FEFK, which was rationally conjugated to an aromatic group naphthoxyacetic acid (Nap) at the N-terminal end to tune its gelation behavior. Interestingly, the presence of oppositely charged amino acids in the peptide amphiphile resulted in pH-responsive behavior, leading to the formation of hydrogels over a wide pH range (2.0-12.0); however, their structures differ significantly at the nanoscale. Thus, by simply manipulating the overall charge over the exposed surface of the peptide amphiphiles as a function of pH, we were able to access diverse self-assembled nanostructures within a single gelator domain. The charged state of the gelator at the extreme pH (2.0, 12.0) led to a thinner fiber formation, in contrast to the thicker fibers observed near the physiological pH owing to charge neutralization, thus promoting the lateral association. Such variation in molecular packing was found to be further reflected in the variable mechanical strengths of the peptide hydrogels obtained at different pH values. Moreover, the gelation of the peptide at physiological pH offers an additional advantage to explore this hydrogel as a cell culture scaffold. We anticipate that our study on controlling the self-assembly pathway of the ionic complementary peptide amphiphile can be an elegant approach to access diverse self-assembled materials, which can expand the zone of its applicability as a stimuli-responsive biomaterial.

Current Progress in Cross-Linked Peptide Self-Assemblies

Peptide-based fibrous supramolecular assemblies represent an emerging class of biomaterials that can realize various bioactivities and structures. Recently, a variety of peptide fibers with attractive functions have been designed together with the discovery of many peptide-based self-assembly units. Cross-linking of the peptide fibers is a key strategy to improve the functions of these materials. The cross-linking of peptide fibers forming three-dimensional networks in a dispersion can lead to changes in physical and chemical properties. Hydrogelation is a typical change caused by cross-linking, which makes it applicable to biomaterials such as cell scaffold materials. Cross-linking methods, which have been conventionally developed using water-soluble covalent polymers, are also useful in supramolecular peptide fibers. In the case of peptide fibers, unique cross-linking strategies can be designed by taking advantage of the functions of amino acids. This review focuses on the current progress in the design of cross-linked peptide fibers and their applications.

Ultrashort Peptide Self-Assembly: Front-Runners to Transport Drug and Gene Cargos

The translational therapies to promote interaction between cell and signal come with stringent eligibility criteria. The chemically defined, hierarchically organized, and simpler yet blessed with robust intermolecular association, the peptides, are privileged to make the cut-off for sensing the cell-signal for biologics delivery and tissue engineering. The signature service and insoluble network formation of the peptide self-assemblies as hydrogels have drawn a spell of research activity among the scientists all around the globe in the past decades. The therapeutic peptide market players are anticipating promising growth opportunities due to the ample technological advancements in this field. The presence of the other organic moieties, enzyme substrates and well-established protecting groups like Fmoc and Boc etc., bring the best of both worlds. Since the large sequences of peptides severely limit the purification and their isolation, this article reviews the account of last 5 years' efforts on novel approaches for formulation and development of single molecule amino acids, ultra-short peptide self-assemblies (di- and tri- peptides only) and their derivatives as drug/gene carriers and tissue-engineering systems.

A review on recent advances in polymer and peptide hydrogels

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.

Tuning the Supramolecular Structure and Function of Collagen Mimetic Ionic Complementary Peptides via Electrostatic Interactions

Collagen, the most abundant component of natural ECM, has attracted interest of scientific communities to replicate its multihierarchical self-assembling structure. Recent developments in collagen mimetic peptides were inclined toward the production of self-assembling short peptides capable of mimicking complex higher order structures with tunable mechanical properties. Here, we report for the first time, the crucial molecular design of oppositely charged collagen mimetic shortest bioactive pentapeptide sequences, as a minimalistic building block for development of next-generation biomaterials. Our rational design involves synthesis of two pentapeptides, where the fundamental molecular motif of collagen, that is, Gly-X-Y has been mutated at the central position with positively charged, lysine, and negatively charged, aspartate, residues. Depending on their overall surface charge, these peptides showed high propensity to form self-supporting hydrogel either at acidic or basic pH, which limits their biomedical applications. Interestingly, simple mixing of the two peptides was found to induce the coassembly of these designed peptides, which drives the formation of self-supporting hydrogel at physiological pH and thus enhanced the potential of exploring these peptides for biomedical purposes. This coassembly of ionic peptides was accompanied by the enhancement in the mechanical stiffness of the gels and reduction in overall zeta potential of the combined hydrogel, which provides the evidence for additional electrostatic interactions. Furthermore, the thixotropic nature of these gels offers an additional advantage of exploration of designer biomaterials as injectable gels. The nanofibers of coassembled hydrogel were found to be highly biocompatible to the fibroblast cells compared to the individual peptides, which was evident from their cytotoxicity studies. We anticipate that our rational design of ECM protein mimics in the form of short bioactive peptides will contribute significantly to the development of novel biomaterials and play a crucial role in the field of tissue engineering and regenerative medicines.

Mechanoresponsive, proteolytically stable and biocompatible supergelators from ultra short enantiomeric peptides with sustained drug release propensity

This report describes the discovery of a set of decanoic acid based amphiphilic derivatives that serves as a template for the stabilization of hydrogel nanoparticles for the sustained release of model drugs.

Designing a bioactive scaffold from coassembled collagen–laminin short peptide hydrogels for controlling cell behaviour

Exploring the potential of bifunctional collagen–laminin mimetic peptide based co-assembling gels for cell culture applications.